node.js - How to get console.log line numbers shown in Nodejs?

Question

Got an old application, that prints out quite a lot of messages using console.log, but I just can not find in which files and lines console.log is called.

Is there a way to hook into the app and show file name and line numbers?

Answer 1

Having full stack trace for each call is a bit noisy. I've just improved the @noppa's solution to print only the initiator:

['log', 'warn', 'error'].forEach((methodName) => {
  const originalMethod = console[methodName];
  console[methodName] = (...args) => {
    let initiator = 'unknown place';
    try {
      throw new Error();
    } catch (e) {
      if (typeof e.stack === 'string') {
        let isFirst = true;
        for (const line of e.stack.split('
')) {
          const matches = line.match(/^s+ats+(.*)/);
          if (matches) {
            if (!isFirst) { // first line - current function
                            // second line - caller (what we are looking for)
              initiator = matches[1];
              break;
            }
            isFirst = false;
          }
        }
      }
    }
    originalMethod.apply(console, [...args, '
', `  at ${initiator}`]);
  };
});

It also patches other methods (useful for Nodejs, since warn and error don't come with a stack trace as in Chrome).

So your console would look something like:

Loading settings.json
   at fs.readdirSync.filter.forEach (.../settings.js:21:13)
Server is running on http://localhost:3000 or http://127.0.0.1:3000
   at Server.app.listen (.../index.js:67:11)